1. Field of the Invention
The present invention relates to a system and method of controlling torque of plural variable displacement hydraulic pumps in construction equipment that drives working devices by operating an engine and the plural variable displacement hydraulic pumps associated with the engine, which can make it possible to use all the set amount of torque regardless of the load pressure or the number of hydraulic pumps.
More particularly, the present invention relates to a system and method of controlling torque of plural variable displacement hydraulic pumps in construction equipment that operates the plural variable displacement hydraulic pumps by an engine, which can control torque of the variable displacement hydraulic pumps so that the total amount of torque of the hydraulic pumps does not exceed the preset amount of torque by presetting the torque so that the engine does not stop even at maximum load of the hydraulic pumps or by presetting the speed of the engine or the used torque of the hydraulic pumps in consideration of the fuel economy or working speed.
2. Description of the Prior Art
A conventional torque limiting control system for a hydraulic work machine is disclosed in U.S. Pat. No. 5,951,258. The conventional torque limiting system, which is also called an apparatus for controlling an electrohydraulic system of a work machine having an engine that drives variable displacement pumps, includes a pump displacement setting device 125 adapted to produce a pump command signal indicative of a desired displacement of the variable displacement pumps 115 and 120; pressure sensors 130 and 131 adapted to detect the fluid pressure associated with the variable displacement pumps 115 and 120 and produce a pressure signal indicative of the detected fluid pressure; an engine speed sensor 140 adapted to detect the speed of the engine 110 and produce an actual engine speed signal indicative of the detected engine speed; torque computing means 205 receiving the pump command and pressure signals of the variable displacement pumps 115 and 120, responsively computing the torque demand on the engine 110, and producing a torque demand signal; torque limiting means 210 receiving the torque demand and engine speed signals, responsively determining a torque limit associated with the engine 110, and producing a specified torque limit signal; and a scaling means 225 receiving the pump command and torque limit signals, determining a scaling factor, and modifying the pump command signal in response to the scaling factor to govern the engine torque.
In the case of scaling the flow rate by using the ratio of an expected torque to the limited torque in the torque limiting control system for a hydraulic work machine, the efficiency of the pump torque in the modified flow rate differs from the efficiency of the pump torque when the expected torque is calculated before the flow rate is modified, and thus the torque limit of the basically causes error occurrence.
Also, there is a limit to individual torque limiting for the plural hydraulic pumps.
In the case of mechanically limiting the torque of the pumps in the conventional torque limiting control apparatus for mechanical variable displacement pumps as illustrated in FIG. 1, the torque limiting mechanism is constructed by a mechanical combination, and thus the maximum torque set for the whole pressure regions cannot be used due to the limitation of the mechanical characteristic even for a single hydraulic pump (In FIG. 1, “a” denotes the flow rate per pressure for the mechanical torque limit, and “b” denotes the ideal flow rate per pressure for a constant torque value).
Also, in the case of performing cross-sensing torque control of plural pumps, the corresponding construction is complicated, and it becomes impossible to use the total amount of torque or 100% of the set torque of the respective pumps.
Also, in compliance with the market requirements, such as fuel economy improvement of the construction equipment, implementation of electronic functions of construction equipment in diverse working environments, and the like, it becomes immediate to adopt electronic hydraulic pumps.
Even in the case of controlling fuel injection to the engine for urgent load, the delay of the engine itself occurs, and the increase of the engine torque is limited by limiting the fuel injection ratio in order to reduce black smoke in compliance with the waste gas regulation.
In addition, trouble may occur in torque matching due to the year elapse of the engine or pumps. That is, in the case of urgent load of the engine, the engine may instantaneously stop or the engine speed may be excessively reduced to cause the output horsepower (hp) of the pumps to be reduced. Also, even in a static state, trouble may occur in torque matching, and in this case, an excessive lowering of engine revolution may continuously occur.